Study Of Biomass Chemical-looping Gasification With Synthetic Cu-Fe Metal Oxides As Oxygen Carriers

Due to the overuse of fossil fuels, greenhouse effect and environment pollution have become increasingly serious. The development of new and renewable clean energy sources, looking for high efficiency and low pollution energy utilization is imminent. Biomass as a carbon neutral renewable clean energy resource, its utilization is very valuable to be developed. It is a good choice for the biomass to be used in the preparation of synthetic gas because of its large amount of hydrogen content, high volatile and easy pyrolysis. CLC technology has many advantages such as inherent CO₂ separation and inhibition of thermal NOX formation when compared with the traditional combustion technology. Chemical-looping gasification?CLG? is a novel technique to generate synthesis gas utilizing similar principles as CLC. The difference lies in that the product of CLG desired is not heat but synthesis gas, a mix of H₂ and CO. In this paper, with synthetic Cu-Fe metal oxides as oxygen carriers we carry out the study of biomass chemical-looping gasification from three major aspects of the performance of oxygen carrier, the optimization of biomass gasification conditions and the analysis of tar.Firstly, thermodynamic simulations and calculations of CuFe₂O₄ reaction with CO, H₂, C and CH₄ showed that the reactivity of oxygen carrier components from high to low in the order of Cu²⁺>Cu¹⁺?Fe³⁺>Fe^8/3+>Fe²⁺. experiment in the thermogravimetric analysis?TGA? proved that CuFe₂O₄ has stable oxygen release characteristics and the cycle stability when reaction with CO.Secondly, experiments of biomass as fuel with five synthetic Cu-Fe metal oxides as OC were performed by thermogravimetric analysis?TGA? and a batch fluidized-bed reactor. It showed that Cu oxides can not only increase the reactivity of the oxygen carrier but also improve the regeneration performance of the oxygen carrier, and appropriate introduction of Fe oxides can improve the anti sintering ability of oxygen carrier. Cu oxides and Fe oxides exhibited good synergistic effect in enhancing the comprehensive properties of the oxygen carrier. By comparing the gas components, gas yield, carbon conversion efficiency, gasification efficiency and tar yield of the five CuFe oxygen carriers using in biomass gasification, it was found that Cu5Fe5 showed better property, which was most suitable for chemical-looping gasification.Thirdly, the condition optimization experiments were performed in a batch fluidized-bed reactor.The results showed that the property was optimal when the S/B was 0.75, the temperature was 800?, the O/B was 0.4 and the oxygen carrier was Cu5Fe5.Finally, tar collected in the condition optimization experiments was detected through GC-MS which found that the addition of water vapor, the increase of temperature and the addition of oxygen carriers could promote the transformation of tar molecules. Moreover, Cu oxides can reduce the tar yield mainly by reacting with the small molecules, and Fe oxides can catalyze the conversion of large molecules to small molecules.